It is know, particularly in electrical heaters, to have a system provided with two electrical heating elements and a thermostatic control for each of the heating elements. Many of these heating systems include a switch arrangement for switching between a first heating element for producing a reduced level of heat and a second heating element or combination of heating elements for producing a higher level of heat. Typically, a rocker type switch is used to switch from the low heat output to the high heat output. For example, this type of arrangement is used in a 1500 watt heater having a 1000 watt output setting and a 1500 watt output setting.
In our prior patents U.S. Pat. Nos. 6,624,397 and 6,940,051 a heating element arrangement is shown where a fan motor is associated with the heating element and the speed of the fan motor automatically adjusts to operate at a low speed under low heat output conditions and to operate at a higher speed under high heat output conditions.
In an earlier portable 1500 watt heater, two separate thermostats are mechanically connected by a gear train such that a single control knob is used to control each of the two separate thermostats. In this way the thermostats are moved in synchronization with each other and are designed to be activated at slightly different temperatures. With this arrangement, a first set of contact points make an electrical connection at a first temperature and activate a low output heating element. If this heating element is sufficient to bring the room temperature up to a particular level then this first thermostat will cut out. If the temperature continues to drop in the area being heated the second thermostat will be activated providing power to an additional heating element. With this arrangement, a user adjusts a single control knob and the two thermostats are maintained in synchronization due to the mechanical gearing of the rotary temperature actuators of each thermostat. Each thermostat is separate and distinct. This portable heater also uses the variable fan speed disclosed in U.S. Pat. Nos. 6,624,397 and 6,940,051.
Therefore this prior art heater allows operation at a lower heat output initially and automatic operation at a higher output if the temperature continues to fall. A problem with this arrangement is the time required to set up and calibrate the two thermostats. An intermediary gear can be provided between gears of each temperature actuator to allow synchronization adjustment between the thermostats. Each individual thermostat is typically calibrated when it is manufactured however the gear train accommodates synchronization between the two thermostats.
For example one of these thermostats may make contact if the room temperature is 4° F. below a particular set temperature level whereas the second thermostat is activated when the temperature drops below 8° F. from the set temperature level.
The present invention seeks to provide an improved thermostat which is cost effective to manufacture and allows convenient calibration and adjustment.